This invention relates to optical fibers, and, more particularly, to the fusion splicing and fire polishing of optical fiber segments to achieve a strong joint.
Glass fibers for optical information transmission are strands of glass fiber processed so that light transmitted through the fiber is subject to total internal reflection. A large fraction of the incident intensity of light directed into the glass fiber is received at the other end of the fiber, even though the glass fiber may be hundreds or thousands of meters long. The glass fibers are fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, and processing the preform to a fiber. The optical glass fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage, and the resulting coated glass fiber is generally termed an "optical fiber" in the art. As an example of its dimensions, in a typical configuration the diameter of the glass fiber is about 125 micrometers, and the diameter of the glass fiber plus the polymer buffer (the optical fiber) is about 250 micrometers (approximately 0.010 inches).
For some applications the optical fiber must be many kilometers long, and must have a high degree of optical perfection and strength over that entire length. Preparation of an optical fiber of that length having no defects is difficult. It is therefore common practice to prepare shorter optical fiber segments of acceptable quality and then splice the ends of the optical fiber segments together to achieve an optical fiber of the required length.
The splicing operation is therefore of critical importance to obtaining optical fibers of sufficient length for these applications. Current splicing procedures typically involve aligning the ends of the optical fiber segments, and fusing them by heating in an electrical arc discharge. Such techniques are generally successful in producing an end-to-end splice of acceptable optical quality. However, the longitudinal strength of the resulting spliced optical fiber is much less than that of the original unflawed optical fiber segments, with failure typically occurring at or near the splice. For example, when optical fiber segments having an axial breaking load of about 15 pounds are spliced together by conventional techniques, the resulting spliced optical fiber may have an axial breaking load of only 1-4 pounds. Since the loading to which the optical fiber may be subjected during service is determined by the lowest breaking stress along the length of the optical fiber, much of the potential strength value of the optical fiber is lost due to the presence of the weak splice.
There is an ongoing need for understanding the origin of the premature failure in the region of the splice between two optical fiber segments, and for a splicing technique that provides improved strength of the spliced region and thence the optical fiber. The present invention fulfills this need, and further provides related advantages.